Micro-hybrid vehicles are being developed for two primary purposes: (1) reducing carbon-dioxide emissions; and (2) reducing fuel consumption. In most micro-hybrid vehicles, fuel economy is typically improved by about 5 to 10 percent because the vehicle includes stop-start technology that stops the internal combustion engine, and its burning of fuel, when the engine's operation is not required (i.e., when the vehicle is stopped).
Vehicles built with a micro-hybrid architecture de-couple the starter motor from the key ignition switch. The starter is controlled by an engine control module that coordinates the stopping and starting of the engine at the appropriate times. In operation, the engine control module will shut off the engine when the vehicle slows down or comes to a stop. When it is time to restart the engine (e.g., brake pedal released, low battery, cabin comfort or other customer satisfaction or safety related need), the engine control module activates (closes) a starter relay, which then provides an electric circuit path that energizes the starter motor.
A relay failure (e.g., when the contacts are welded in the closed position), however, would result in the starter motor being continuously powered. This could be a dangerous situation. Thus, when the starter relay fails, the engine control module must revert to an “engine always on” mode of operation to avoid potential damage to the starter motor, flywheel or flex plate ring gear and to allow the vehicle to be safely driven to a service facility.
Accordingly, there is a need and desire for a diagnostic mechanism for detecting a vehicle starter relay failure.